Rolling of metal powders by directly feeding them into the roll-gap or nip of a rolling mill, has been demonstrated as a commercial process for making wrought metal strips of various metals and alloys. Broadly, the process involves roll compaction of the desired metal or alloy powder, followed by strand or coil sintering, rerolling (cold), resintering and finish rolling. Commercial processes based on this general principle are in use for making strips from nickel powder, cobalt powder, iron-nickel alloy powders, etc. The key steps in these processes are: (a) roll compaction of the powder which should result in a continuous greenstrip having sufficient green strength for subsequent processing and uniform green density, and (b) sintering of the roll compacted green strip to achieve sufficient interparticle bonding so that the strip can withstand subsequent densification by cold rolling. Typically, the roll compacted green strip will have a density in the range of 72 to 82% of the theoretical full density.
A variation of the above described powder rolling process also exists, in which the roll compacted strip is hot rolled to achieve full theoretical density, instead of sintering and cold rolling. However, this approach is not very practical (and hence is rarely practiced commercially) due to the facts that (a) extreme care must be taken to prevent the porous green strip from getting oxidized either during pre-heating or hot-rolling (the entire hot rolling stand would be required to be kept under controlled atmosphere) and (b) it is difficult to achieve a precise matching of the speeds of the two rolling mills, without which the porous unsintered strip will be pulled apart.
Direct powder rolling of dispersion strengthened copper powder poses some unique problems as compared to metals and alloys that are currently processed by powder rolling. The major difference lies in the fact that dispersion strengthened copper powder does not sinter nearly as well as these other metal and alloy powders do. Dispersion strengthened copper powder consists of a Al.sub.2 O.sub.3 rich layer on the surface of the particles (which inherently develops during the internal oxidation step) that prevents sintering. Additionally, the Al.sub.2 O.sub.3 dispersoids present in the matrix of the material prevent grain growth even at very high temperatures, which affects sinterability.